1. Field of Utilizing the Invention
This invention relates to a method of driving an optical modulation device such as a ferroelectric liquid crystal panel, which has a memory function and is used as a display device.
2. Description of the Prior Art
Recently, demand has increased for a thin, or flat, display device having a large display capacity in the field of information equipment represented by the computer and in the field of visual equipment represented by the television, video tape recorder and video disc player. The ferroelectric liquid crystal panel is an example of such a flat display device.
A matrix driving method for a ferroelectric liquid crystal panel, which is a slight modification of an in-field AC optimized amplitude selection scheme used for a nematic liquid crystal is shown in SID 85 DIGEST (1985), pp. 131-134, "An Application of Chiral Smetic-C Liquid Crystal to a Multiplexed Large-Area Display" by T. Harada et al. A one-display-area rewriting period (one frame) is divided into two fields different in polarity from each other, in which an on-state (or off-state) is set in a first field, and an off-state (or on-state) is set in a second field. In this method, however, off-pixels (or on-pixels) are not written in the first field, so that a flicker is noticeable and it takes a long time for rewriting the image in the whole display-area.
A method of scanning a plurality of scanning lines at the same time is shown in a Japanese paper "Simple Matrix LCD using Convolution Scanning Method", Hiroaki IDENO, EID 86-22 (1986), pp. 25-28. This method uses a convolution scanning method for driving a nematic liquid crystal display with a high contrast. However, this method would reduce resolution when applied to a ferroelectric liquid crystal.
Another method of scanning a plurality of scanning lines at the same time is shown in Japanese Patent Publication No. 61-243430 (1986), "Method of Driving a Ferroelectric Liquid Crystal Elements". This method divides the scanning lines into a plurality of blocks and drives the scanning lines block by block. This method requires a line memory capable of storing display data for the pixels connected to scanning lines in one block and a complicated driving circuitry.